Transforming growth factors (TGFs) are hormonally active polypeptides capable of inducing a transformed phenotype when added to normal, non-neoplastic cells. TGFs are found in certain normal tissues and in many retrovirally-transformed and tumor-derived cell lines. The first aim of this project was to identify and isolate TGFs produced by transformed cells. We have found that culture fluids from feline sarcoma virus-transformed cells contain two different factors, TGF-alpha and TGF-beta that, when acting in combination, induce acute phenotypic transformation in rat fibroblasts. Both factors have been purified to homogeneity and characterized. TGF-alpha is a 6.0 kilodalton polypeptide with limited (33 to 44%) amino acid sequence homology to epidermal growth factor (EGF). TGF-alpha and EGF are potent mitogens which, when acting alone, have weak transforming action. The transforming activity of TGF-alpha and EGF is strongly potentiated by TGF-beta. TGF-beta purified from the same cell line that produces TGF-alpha is a 23 kilodalton, disulfide-linked dimer that consists of two 11 to 12 kilodalton subunits. TGF-beta does not induce phenotypic transformation when acting alone. Our second aim was to identify the cell surface receptors mediating the action of TGFs. We have identified the receptor for TGF-alpha as being the same as the receptor for EGF, a 150 to 170 kilodalton membrane glycoprotein with associated tyrosine kinase activity. Despite their limited structural homology, TGF-alpha and EGF exhibit similar affinity for binding to this receptor type and a similar potency to activate the receptor-associated protein tyrosine kinase and to down-regulate the receptor. It has been found that the EGF/TGF-alpha receptor is a target for rapid modulation by TGF-beta. We have also characterized the ligand binding properties and the dynamics of cellular receptors for TGF-beta. The subunit structure of the TGF-beta receptor has been determined using receptor affinity-labeling methodology. We are currently addressing the biochemical actions of TGF-beta at the cellular level. (J)